The S&W manual states to "lower the yellow sear deactivation lever" when field stripping the Shield, and to "...verify that the yellow sear deactivation lever is in the lowered position; it must be protruding into the magazine well..." prior to sliding the slide back on.

I have seen videos where people do not lower the sear deactivation lever and just pull the trigger to release the slide, and when reassembling the weapon, I have NEVER seen anyone lower the sear deactivation lever prior to sliding the slide back in place.

So...I am confused. Can this damage the gun? I am no technical weapons expert by any means, but I do want to understand/know the inner workings of my weapon and why they are designed as they are. Thank you in advance.

People will always come up with shortcuts or try to find a better way of doing something. Why question the Owner's Manual? It was written for a purpose and should be followed. You can disassemble it just like a Glock, but then quite a few Glocks have gone BANG and left a hole in the kitchen floor because someone forgot to clear the gun. You Tube is no substitute for the Owner's Manual.........

What Lee said.

The owners manual for your car tells you to turn off your car and put it in park when you're done with it. Would you just leave it running and kick a brick under the tire instead?
Don't pull the trigger. Use the SEAR lever.
No accidental BANG that way.

To actually answer your question, no, this will not damage the gun. The sear deactivation lever (and instruction to use it in the manual) is simply S&W's way around liability in case you don't have the sense of mind to check your chamber each and every time you disassemble your gun.

Rule #1 to disassembling a firearm: personally make sure it's chamber is cleared and ammunition is removed.

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M&P40c/15-22/SD9VE/Mossy500

I never use the lever. The lever is an added safety, to eliminate someone from pulling the trigger with a round in the chamber. What did people do before they started installing the sear deactivation lever? They used common gun safety and insured there was no live round in the chamber, prior to pulling the trigger. I would hope those that use the lever would still check the chamber first, to make sure there is no ammo loaded. But if you use proper gun safety and check that you weapon does not have a round in the chamber (along with no loaded magazine), then there would never be an issue by pulling the trigger, instead of using the sear deactivation lever. I also do not put my car in reverse and start backing, without looking rearward first, but I am sure there are some that do. Safeties are added to prevent accidents, which in most cases would be prevented if proper gun safety is followed. Name a safety that is necessary. Even the "drop safety" is not necessary, if you insure that you never drop your gun. However with the nature of us human beings, we do need extra help to prevent accidents, and that is why those safeties have been added to the guns.

To the OP question. No you will not do any damage to the gun by not using the lever, whether removing or installing the slide.

Bob

I can't speak to the Shield but I've done the trigger pull on my FS M&P9. Mine is a bit more involved since I have the mag safety.

The only difference i see is that if I use the lever, it stays down until I insert a mag. When I reinstall the slide, the striker ends up uncocked. If i do the trigger pull, the striker ends up cocked.

While I have practiced doing it with the trigger pull (just in case), I rely on the lever for routine maintenance.

I use both methods. Since I check & double check the chamber before I squeeze the trigger & since I've carried Glocks for years & owned a Sigma it's just habit for me.

A word of advice - use something other than the tool in the grip for lowering the sear deactivator lever. Many have complained about wearing the little knob off of it. I normally use a pen or pencil, anything other than the tool.

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Former USN, Retired US Army

I would agree with this. I've used the tool but it's a bit of a pain to remove (mine's really tight). That's why I practice with the trigger pull in case I need to do this "in the field".

However, in my case, that's unlikely. So I use whatever is handy, pen, tweezers, awl, even parts of my cleaning kit.

YMMV.

You will not damage your gun. In fact, short of using the gun in a manner not intended, it is very difficult to damage an M&P.

Rob and I disagree on this point:
I always use the lever.

By using the lever it is impossible to set off a live round. Even if the user were bone headed enough to forget to check the chamber, it can't be fired. Why? Because the sear is down and the striker is not cocked. Thus, the gun won't fire.

I don't use the "pull the trigger" method nor do I teach it in my class. Why circumvent a simple safety? I can move the lever with my pinkie nail, no tool necessary.

People are correct, if you check the chamber, if you point in a safe direction, if you're being conscientious, you won't have an ND. That's a lot of 'ifs'. So, I like the one 'if'. If you move the lever you can take off the slide. I prefer the poka-yoke or mistake proofed way.

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Freedom isn't free.

The sear deactivation lever was specifically designed to allow owners/users to be able to release the striker without having to pull the trigger. This isn't an inconsequential feature to be able to provide to potential LE users, so the pistol line that eventually received the resurrected name of "Military & Police" had it incorporated. Obviously, S&W doesn't recommend releasing the striker by pulling the trigger, but by using the sear deactivation lever.

Now, as to having to make sure the lever is lowered in order to install the slide & barrel? If I had to guess, I'd lean toward it being because of how the lever was originally designed, and how the manual was probably originally written.

The original lever had a dog-leg angle and was "shorter". The angle made it easier to move with a tool or pin punch to release the striker for field-stripping, but it also introduced an unexpected potential problem. If it wasn't left in the down position, it could get in the way during reassembly (the slide's pick-up rail would catch against it).

By straightening the lever, it cleared the slide's pick-up rail during reassembly if it was inadvertently put back in the raised position. (It slips beside the pick-up rail.) Yes, it did make it a bit less easy to initially catch and depress the straight lever (without practice).

This picture shows an old (original) style sear deactivation lever on the left, and the new (current) style on the right.


Basically, after the pistol was released they discovered they needed to make the change to that lever to help make reassembly after field-stripping more "cop proof".

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Ret LE Firearms inst & armorer

Ah, no. A recent check of NYPD stats showed that 75% of the AD/ND/UD incidents happened during what we'd call routine handling: loading, unloading and "cleaning". Fully half of those incidents involved personal injury.

The intent was to make it extemely difficult for someone to contribute to those stats.

However, there's always the tendency to take shortcuts. That being the case, the individual involved owns the entire responsibility for the incident.

Ah, yes. If S&W's field stripping instructions were to pull the trigger, it most definitely could be a liability for them, as you can file suit for a lot of things if there is even a hint that it could have been avoided. (Remember the McDonald's coffee incident?) Despite the instructions to ensure your gun is unloaded and cleared.

I agree though, that it should be on the individual handling the gun. There's simply NO excuse to not have checked your chamber. I see the sear deactivation lever as akin to a calculator, in that it's simply another device to allow people to NOT use their brain. Seems society wants to rely on safety measures to prevent bad things from happening, yet all it does is prevent people from being truly educated about any given subject. (i.e. "who needs to be able to read a map? I have GPS", or "who needs to learn how to tie shoes? I have velcro or slip-ons")

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M&P40c/15-22/SD9VE/Mossy500

I probably should have said that the lever eliminates any need to pull the trigger, although what I said/typed is true. There were a lot of highly placed police administrators who were thrilled that the M&P designs had the sear lever. [I don't know that S&W did any focus groups prior to starting design or during design. "What would you want/not want in a service pistol?"]

I don't recall any weapon prior to Gastons Gadget that had "pull the trigger" as part of the field strip directions. In any case, it was a really poor decision on the part of the design team (or teams if there were predecessors). We beat on the fact that firearms are mechanical devices and they don't care what your intent was. If there's a round present, there will be a loud noise.